An earthquake along the Hayward Fault jolted Bay Area residents out of bed shortly before 3 a.m.
Initially recorded as a magnitude 4.7 temblor, it was quickly downgraded to 4.4.
Though there were no immediate reports of significant damage, the tremor at 2:39 a.m. was felt as short-duration shaking -- typically five seconds or less -- around the Bay Area. Residents close to the epicenter near Berkeley's historic Claremont Hotel reported alarming degrees of shaking. TV meteorologist Roberta Gonzales was among callers who told KCBS that it felt as though their homes were "picked up and dropped." Others described a rolling sensation.
Commuters were advised to expect early-morning delays on BART to allow time for routine track inspections.
USGS geologist David Schwartz says the quake occurred within about a 5-mile section of the Hayward Fault that has been active, with numerous quakes of magnitude 3 to 4 over the past decade.
"It's a hot spot on the Hayward Fault," Schwartz told KQED.
The Hayward Fault runs along the western edge of the East Bay hills, from San Jose into the North Bay. The last major quake on the fault broke with magnitude 6.8 in 1868. Five fatalities were recorded. According to USGS, it is "very likely that the Hayward Fault will rupture and produce a significant earthquake within the next 30 years."
Schwartz says you would typically start to see damage from quakes in the magnitude 5.5 range -- but that Thursday morning's event was a wake-up call in more ways than one.
"This is a mid-4 quake and it's felt all around," notes Schwartz. "So imagine if we had a 7. This is just a little sample of what to expect down the road."
Ted Goldberg of KQED News contributed to this report.